64 WILSON & TOOMER FERTILIZER COMPANY 



tion, being one-celled plants and so tiny 25,000 could be 

 placed side by side in a line an inch long. However, the 

 multiplication of bacteria under favorable conditions is 

 beyond our conception, and what they lack in size is made 

 up in numbers. Favorable conditions for the develop- 

 ment of one form of bacteria may be most unfavorable 

 for another; the most noticeable distinction being that 

 some (aerobic) require an abundant supply of air, 

 while others (anaerobic) flourish where the circulation 

 of air is limited. Certain conditions are unfavorable to 

 all bacteria: dry sandy soils lacking in humus contain 

 very few; pure clay soils are equally barren; and also 

 any soil that is filled with stagnant water or that is 

 strongly acid. Many bacteria are killed by drying, 

 while others only remain dormant. It has been found 

 that in the decomposition of vegetable matter there is 

 very little bacterial action when the moisture drops below 

 twent^^-five per cent. 



Bacteria, like root hairs, take food by absorption 

 through the cell Avails, therefore, only dissolved sub- 

 stances can be used. To aid in this solution the bacteria 

 give off secretions called "enzymes." Enzymes are 

 strictly chemical substances which break down organic 

 compounds but do not enter into combination. Organic 

 matter is complex and the various changes are not fully 

 understood, but either the enzymes themselves or the com- 

 pounds they induce, or perhaps both, are under some cir- 

 cumstances "highly useful," but under others they are 

 "intensely poisonous" because conditions govern the 



